As a result of search for systems which have aggregate structures, the displacement reaction products of Ti with CoO or NiO are found to have aggregate structures in which the produced oxides and metals are entangled with each other. The displacement reaction of Ti with CoO or NiO is investigated at the temperature of 1273K. In the reaction of either couple, aggregate products are produced, and reacted layer is observed in the TiO2 matrix wherein Co or Ni phases are three dimensionally entangled in finely dispersed state of micron order. 2 layers of cavitated and dense TiO2 layers are found in the reacted layer. The thicknesses of the reacted layer are not constant according to locations, but thick portions are grown obeying the parabolic rate law. As a result of the study on the possibility of fabricating cermet by the reaction between powders, finely mixed characteristic structures are found to be easily obtained using systems which can produce aggregate structures. 24 refs., 9 figs.